During deposition in a processing chamber, a film can be deposited on a frontside of the wafer. For example, in atomic layer deposition (ALD), a film can be deposited layer by layer by successive dosing and activation steps. In ALD processing chambers, precursor gases can be directed to a wafer and the precursor gases can chemisorb onto a surface of the wafer to form a monolayer. Additional precursor gases can be introduced that react with the monolayer, and a purge gas can be subsequently introduced to remove excess precursors and gaseous reaction by-products. Precursor gases can be alternately pulsed without overlap, and cycles can be repeated as many times as desired to form a film of suitable thickness.
However, when the wafer is held by a chuck-less method, wafer slippage can occur and lead to non-uniform thickness of the deposited film at a wafer edge. For example, during the deposition process, the wafer can be supported on wafer supports which provide a gap between the wafer and the pedestal upper surface and a gas cushion in the gap can lead to wafer movement (slippage) such that the wafer moves closer to one edge of a pocket in which the wafer is located. If the wafer is not centered in the pocket, the film thickness can be non-uniform at the water edge.
Accordingly, it would be desirable to provide a solution to the problem of wafer slippage during film deposition in order to improve azimuthal thickness uniformity at the wafer edge.